One of the byproducts of fuel combustion in an internal combustion engine is carbon particles, which are typically referred to as soot. Emission standards typically specify a limit to the amount of soot that an engine can emit to the environment, which limit is typically below the level of soot generated by the engine during operation. Therefore, various components and systems are employed by engine or vehicle manufacturers to control and limit the amount of soot emitted to the environment.
One device commonly used to limit the amount of soot expelled into the environment from an engine is referred to as a particulate trap or diesel particulate filter (DPF). Such a device includes a porous substrate, for example, made of ceramic material, that may be coated with various chemical compounds that alter the composition of exhaust constituents. The porosity of the substrate acts as a filter for physically trapping carbon particles or soot in an exhaust stream passing over and/or through the filter. One can appreciate that such physical removal of carbon particles from a gas stream will progressively saturate the filter with particulate matter.
A typical DPF is made of a collection of elongate filter elements arranged in bundles. Each filter element has a generally tubular shape and a polygonal cross section, for example, hexagonal or octagonal. The filtering elements are usually bundled together into a larger, typically cylindrically shaped filter, which has a generally beehive cross sectional shape. The internal surfaces of the filter elements collectively provide a relatively large surface area onto which soot and ash particles are collected.
Although soot particles are periodically removed from a DPF by an oxidation process, ash particles cannot be thus removed and collect in the DPF over time. The ash particles are typically the result of burning of lubrication oil in the engine, and their collection on the DPF diminishes the surface area for flow of exhaust gas through the DPF, thus increasing the exhaust gas restriction of the engine, which increases fuel consumption and also increases the frequency of DPF regeneration.